The present invention relates to the fabrication of integrated circuits. More particularly, the invention provides a method and apparatus for controlling the temperature, maintaining the vacuum integrity and facilitating maintenance of a lid assembly for a semiconductor processing chamber.
High density integrated circuits, commonly termed VLSI devices, are typically formed on semiconductor wafers by subjecting the wafers to a number of deposition, masking, doping and etching processes. The wafers are placed on the upper surface of a pedestal or susceptor within a processing chamber, and process gas(es), such as tungsten hexafluoride and silane, are delivered into the chamber onto the wafer to perform the various deposition and etching steps. Typically, the process gases are directed through a manifold and mixed in a water-cooled gas mixing chamber within the manifold head. This cooling is often desired because the process gases may react to form a solid precipitate that deposits onto the walls of the manifold head at temperatures greater than a threshold temperature. After mixing in the cooled manifold head, the gaseous mixture is delivered through a lid assembly that includes one or more gas distribution plates for delivering a uniform distribution of the gaseous mixture into the deposition chamber onto the wafer.
During processing, the gas distribution plates of the lid assembly (i.e., the gas distribution plate or showerhead and the gas dispersion plate or blocker plate) receive heat from the gases flowing therethrough and from the heated wafer in the processing chamber. If these plates reach a threshold temperature, the process gases passing through the gas distribution system may react to form large particulates which clog the gas distribution holes of the plates. In addition, a layer of deposition may form on the inner surface of the plates to later flake off in large particulates that rain down on the wafer to create an uneven deposition layer, thereby contaminating the wafer.
The gas distribution plates of the lid assembly are typically mechanically coupled to a gas injection cover plate and a mounting plate, which are attached to a base plate for mounting to the processing chamber. The interfaces between these components are usually sealed with gas seals (e.g., O-rings) so as to maintain a vacuum-tight seal throughout the lid assembly. During installation of the lid assembly, however, it is often difficult to precisely align the gas seals within the corresponding grooves of the plates. In addition, the gas seal surfaces and grooves can be damaged from handling during this installation. A gas seal that has not been precisely installed or one that has been damaged during installation may contain a leak. This leak allows gas to pass through the lid assembly during processing, thereby disrupting the desired pressure within the processing chamber. Disruption of this desired pressure, which is typically on the order of 1-2 milliTorr, will adversely affect the deposition uniformity on the semiconductor wafer. Therefore, the gas seals must be repaired or reinstalled, or the entire lid assembly must be replaced when the vacuum integrity of its components has been compromised. Frequent reinstallation, repair or replacement of the lid assembly increases the manufacturing cost of the wafers and the downtime of the processing apparatus, which decreases the throughput of the process and further increases the manufacturing cost of the wafers.
Periodic cleaning and maintenance of the exposed surfaces of the processing chamber also increases the downtime of the processing apparatus. For example, the surfaces of the lid assembly that are exposed to process gases are typically cleaned periodically to remove deposition reactant from these exposed surfaces. To accomplish this, the lid assembly usually must be completely taken apart to separate the gas distribution plates from each other and to thereby access the exposed surfaces of these plates. Disassembling the lid assembly for cleaning takes a relatively long time. Moreover, reassembling the lid assembly after cleaning requires the gas seals and the gas distribution plates to be realigned, which can be a difficult, time-consuming process.
What is needed in the semiconductor manufacturing industry, therefore, is an improved lid assembly for a wafer processing apparatus. It would be desirable to maintain the temperature of the various components of the improved lid assembly below a threshold value to thereby avoid reaction and subsequent deposition of the processing gases on these components. In addition, the components of the lid assembly should be designed to minimize leakage of fluids therebetween to maintain a sufficient gas seal over the processing chamber. Furthermore, it would be desirable if the lid assembly were designed to facilitate cleaning of the surfaces that are exposed to process gases during processing.